A substrate such as a wafer can be illuminated, by an illumination module, with multiple electron beams.
A collection module collects multiple collected electron beams that are formed from the illumination of the substrate.
The collection module introduces aberrations to the collected electron beams.
The multiple collected electron beams are converted to multiple light beams by an electron to photon converter. The multiple light beams as well as noise are sensed by a detector.
There is a growing need to provide a detection module that is capable of detecting the multiple light beams despite the noises the aberrations introduced by the collection module.